1. Field of the Invention:
The invention relates to a process for the manufacture of low-viscosity highly concentrated aqueous pastes of alkali metal salts of of .alpha.-sulfonated fatty acid alkyl esters.
2. Description of the Related Art:
Alkali metal salts of .alpha.-sulfo fatty acid alkyl esters are known to be obtained in the form of aqueous pastes by the neutralization of .alpha.-sulfo fatty acid esters with aqueous alkali metal hydroxide. As the industrial starting material, renewable raw materials of natural origin, are increasingly being used, mainly fats and/or oils of vegetable origin, from which the fatty acid alkyl esters are obtained either by ester splitting and subsequent esterification with low alkanols, particularly methanol, or by the transesterification of natural triglycerides with low alkanols. The fatty acid ester mixtures that result--depending on the origin of the natural raw material--contain esters of fatty acids of a comparatively wide carbon number range, which is normally between 10 and 24 for the fatty acid radical. Fatty acid ester mixtures of this type are preferably sulfated with gaseous sulfur trioxide. This results in more or less strongly colored acidic crude sulfonates, which are bleached and converted into ester sulfonate pastes by neutralization to the pH-range of around 6 to 7. In this form they are very important as surface-active agents or wetting agents for washing and cleaning purposes.
A particular difficulty experienced in the industrial handling of these pastes of alkali metal salts of .alpha.-sulfonated fatty acid alkyl esters--known in the following as "ester sulfonate salts"--lies in their concentration/viscosity characteristics. Industrially occurring ester sulfonate salts only form sufficiently mobile, e.g. that can be pumped, solutions or suspension in aqueous admixture, with the low viscosity to still ensure the problem-free running of industrial processes, when they have comparatively low solid concentrations, e.g. solid concentrations of up to about 35% by weight. With higher ester sulfonate salt contents, e.g. solid contents of around 40% by weight or more, the viscosity of the aqueous preparation increases so sharply that it no longer has free mobility. This causes serious limitations: the aim of producing highly concentrated ester sulfonate salt pastes directly by neutralization of the crude sulfonic acid mixture with a concentrated alkali metal hydroxide solution, cannot be achieved because the capacity to be stirred of the mixture and therefore the even mixing of the two components of the reaction mixture (crude sulfonic acid mixture and alkali metal hydroxide solution) is no longer ensured. At the same time therefore it becomes impossible for the neutralization heat to be carried away. Unwelcome secondary reactions occur due to local concentration and temperature peaks. It is disadvantageous apart from this that the ester sulfonate pastes immobilized by the viscosity increase are no longer pumpable in the industrial plant. The blockage of pipes occurs and with it a lasting disturbance of the operation of the entire plant.
The prior art on ester sulfonate salt pastes deals intensively with such peculiarities. To improve the flow behaviour and therefore the industrial ease of handling of this type of paste it has in particular been suggested that flow aids or viscosity regulators are added to the aqueous concentrates of .alpha.-sulfor fatty acid alkyl ester salts obtained on an industrial scale. For example, U.S Pat. No. 4,495,092 depicts the concomitant use of C.sub.8 to C.sub.40 alcohols, which can in addition have one or more hydroxyl groups as substituents and to which up to 20 mol of ethylene oxide and/or propylene oxide per mol of alcohol can be added. These viscosity regulators are added to the ester sulfonate pastes in quantities of 1 to 15% by weight in relation to the amount of ester sulfonate salt such that the viscosity of the ester sulfonate paste adjusts to a maximum of 10 000 mPa.s at 70.degree. C. With a viscosity in this range one can also ensure that the mixture can be pumped.
U.S. Pat. No. 4,675,128 describes the use of alkali metal alkane sulfonates with an average carbon number of 11 to 21 as viscosity regulators for aqueous highly concentrated industrial .alpha.-sulfo-fatty-acid-ester alkali-metal-salt concentrates, which contain at least 30% by weight of the active ester sulfonate salt. The viscosity regulators are used in quantities of 0.5 to 10% by weight referred to the ester sulfonate salt content, and ensure a viscosity at 40.degree. C. of a maximum of 10 000 mPa.s and therefore also pumpability of the ester sulfonate salt concentrates in the industrial field.
According to German Patent Application No. 35 38 910 mobile aqueous pastes of wash-active .alpha.-sulfo fatty acid ester salts can be manufactured from crude sulfonic acids at high temperatures by subjecting the crude sulfonic acids to a subsequent reaction with monovalent alcohols and/or their alkoxylation products before introduction into the aqueous alkali metal hydroxide phase. Preferably, monofunctional alkanols with up to 30 carbon atoms in the alcohol radical are used, or their alkoxylation products with up to 20 alkoxy radicals in the molecule. Also with this process one can obtain ester sulfonate salt pastes that are easily mobile precisely in the critical concentration range of around 35 to 60 % by weight, and which are also easy to process on an industrial scale.
The disadvantages of the solutions proposed by the prior art for the problem of reducing the viscosity of ester sulfonate salt pastes by the addition of alcohols, are to be seen in that the neutralized products of the process contain in high quantities the alcohol that has been added to set low viscosity values. This is undesirable because the short-chained alcohol interferes with the manufacture of detergent mixtures by spray-drying. In particular the undesirable "pluming" (aerosol formation during spray-drying) effect is caused by the presence of the alcohol additives. The free alcohols in the ester sulfonate salt mixture moreover also have an undesirable alien odor and deodorization of the product is therefore necessary. Before the spraying of the aqueous pastes for the manufacture of detergents, it may be necessary for this reason to interpose process stages to drive out the excess alcohol. This however increases the cost of the process as a whole in an undesirable way.
It is an object of the present invention, therefore, to provide a process for the manufacture of ester sulfonate salt pastes in which an improvement of the flow behaviour of the pastes at high active substance concentrations can be achieved. Compounds or mixtures of compounds should be used for the adjustment of the viscosity in this process which have a significant viscosity-reducing effect even in small concentrations. These substances should not however effect, or at least not disadvantageously effect, the properties of the product.
The solution to the problem consists in using compounds known as hydroxy ocenol sulfonates which have the formula ##STR2## wherein X is SO.sub.3 M, Y is OH or X is OH, Y is SO.sub.3 M, and M is selected from the group consisting of hydrogen, an alkali metal ion, an alkaline earth metal ion, or NR.sub.4 wherein R is hydrogen, an alkyl or hydroxy alkyl radical having from 1 to 4 carbon atoms; a and c are integers having a value of from 0 to 18, b is an integer having a value of from 0 to 2 such that the sum of a+b+c is from 12 to 18 alone or in combination with compounds known as hydroxy ocenol ether sulfonates which have the formula ##STR3## wherein X is SO.sub.3 M, Y is OH or X is OH, Y is SO.sub.3 M, and M selected from the group consisting of hydrogen, an alkali metal ion, an alkaline earth metal ion, NR.sub.4 wherein R is hydrogen, an alkyl or hydroxy alkyl radical having from 1 to 4 carbon atoms; a and c are integers having a value of from 0 to 18, b is an integer having a value of from 0 to 2 such that the sum of a+b+c is from 12 to 18; Z is an oxyethylene, oxypropylene, or oxybutylene group; n is an integer having a value of from 1 to 30. The hydroxy ocenol sulfonates and/or hydroxy ocenol ether sulfonates are used in low concentrations in the manufacturing processes as substances for reducing the viscosity, and thus effecting a clear reduction in the viscosity of the aqueous ester sulfonate salt pastes with a high surface active-substance (sulfonate ester salts) content.